Human colostrum contains a population of viable cells including lymphocytes, macrophages, polymorphonuclear leukocytes, and epithelial cells. The ability of colostral lymphoid cells to produce immunoglobulins and release antibodies specific for antigens encountered in the maternal gastrointestinal tract is currently a matter of controversy. While hemolytic plaque formation has been regularly observed it appears that colostral phagocytic cells and noncellular globular elements can store and release milk proteins, including immunoglobulins. The purpose of the studies outlined in this proposal is to characterize the immune capacity of colostral cells and the effect which they exert on peripheral blood lymphocytes in mixed lymphocyte reactions. Unfractionated colostral cells and isolated cell types will be studied for their ability to respond to polyclonal mitogens and specific antigens. Attempts will be made to identify T cells and T cell subpopulations. Peripheral blood lymphocytes will be cultured in the presence of various proportions of colostral cells, colostral cell subpopulations or in the presence of supernatants from colostral cells. Studies will be undertaken to determine what effect the removal of suppressor T cells or inhibition of the release of suppressor factors from colostral cell populations may have on the parameters outlined above. While the significance of the humoral components of clostrum has been stressed in the protection of the neonate, the importance of colostral cells is not well clarified. In addition to the release of passively acquired antibodies in the infant's gastrointestinal tract which may protect the mucosal surface of the baby, the encounter of the neonate with maternal cells of different histocompatibility determinants may have a profound stimulatory or suppressor effect on the development of the immune system and its subsequent reactivity with environmental antigens.